It seems Spotify can't access the information provided on my facebook account that I used to log in. My birthday is wrong and the email address isn't shown. This also seems to lead to an error (see below).
It looks like the following (sorry for German screenshots, but you get the idea):
I already tried to delete the Spotify App from facebook and re-activate it, but this didn't change anything.
I don't have any more ideas how to fix this or how to make the scenario described below work.
The reason why I want this to work:
I need a device password to log in to my account from a device. I cannot create a device password via the Spotify website, because I get the error message that "my email address isn't available".
I also tried to create the password fia facebook (Security -> App Passswords -> Generate App Password -> Create Entry called "Spotify"). I can't log in with the password that is created (I tried it with the number displayed on my profile and the mail address from my facebook account).
EDIT: it seems this works now. While the re-logging on the desktop client didn't add the email address, when I logged in on my phone again via FB the correct address was finally there.